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need to know what the best way to insulate 3 seasin room-walls and ceiling are insulated-floor is not-floor is 10 ft off the ground-built with 2/8s and 2/10sbeen approved by city but they suggest fiberglass and close in bottom-I'm afaid of traping wetness in closed space with no breathing room for moisture??

If you close in the bottom with something like bead-board it will breathe well enough and look good too, so fiberglass will work fine like that. Edge-butted planking can do OK too but it's harder to fit tightly. If you use something that does not allow 'breathing' go with closed-cell foam.